A battery pack typically comprises one or more battery cells that are encased within a housing of the battery pack. During normal operation a battery pack may undergo temperature fluctuations. For example, when power is drawn from the battery pack, the battery pack typically generates heat and the internal temperature of the battery pack may rise. Also, after power ceases to be drawn from a battery pack, heat may dissipate from the battery pack, and the internal temperature of the battery pack may fall.
The battery pack typically contains air that can expand and contract in response to the internal temperature fluctuations. When the internal temperature rises, the air may expand and when the internal temperature falls, the air may contract. Accordingly, if the air is confined to the interior of the battery pack, the pressure of the air can rise and fall with the internal temperature. In some cases, the battery pack will outgas as the internal temperature rises and when the battery pack cools, the outside ambient air of the surrounding environment of the battery pack can enter the battery pack and cause degradation to the internals of the battery pack due to moisture and other non-compliant intrusions. In addition, efficiency of the battery pack may be lessened when the internal air pressure rises or falls beyond a certain value. In some cases, if the internal air pressure rises beyond a critical value, the battery pack may be damaged. For example, the housing of the battery pack may burst, which is dangerous and costly.